Typically, machines, such as motor graders, may include a braking system having two independent braking circuits for increased safety and to conform to statutory regulations. Such a braking system generally includes two separate brake valves or two sections within the same brake valve. Due to design and tolerances, these separate brake valves or valve sections typically result in a pressure bias, i.e., different braking pressures for the two braking circuits. This pressure bias may cause premature brake failure due to higher pressure and resulting higher energy load.
Various solutions are proposed in the prior art to decrease the pressure bias. For example, a mechanical device, such as a by-pass valve, may be provided to reduce the pressure bias. However, using such mechanical devices may increase cost of the braking system. Additionally, the mechanical devices may not be suitable for dynamic changes in pressure bias.
For reference, U.S. Pat. No 4,729,607 discloses a dual circuit brake valve with a delivery differential control mechanism which controls the differential between the delivery pressures of the primary and secondary braking circuits. The delivery differential control mechanism includes a spring retainer which is mounted on the end of the stem of the relay valve and which receives a spring-biased plunger. The plunger engages with the actuating member during the brake application to thereby transfer the force of the spring to the relay member and therefore to the valve members of the secondary circuit. This transfer of the spring force reduces the crack open pressure of the valve members controlling communication through the secondary circuit, to thereby reduce the differential between the pressures generated and the primary and secondary circuits.